The general purpose of this project is to study the immune responses in man and animals to natural and experimental rickettsial infections. Currently, we are studying 1) the prophylactic qualities of rickettsial vaccines against spotted fever, epidemic typhus fever, and Q fever with respect to physical and chemical qualities of the antigens and persistence of protection in experimental animals over protracted periods of time, 2) the effect of age of guinea pigs on their ability to combat rickettsial infections, 3) rickettsial endocarditis caused by Coxiella burnetii, 4) effectiveness of the antibiotic, rifampin, against rickettsiae in cell culture systems, and 5) the possible existence of common antigens in some strains of Chlamydia psittaci and some bacteria including the agent of Legionnaires disease. BIBLIOGRAPHIC REFERENCES: Ormsbee R., Peacock, M., Philip, R., Casper, E., Plorde, J., Gabre-Kidan, T., and Wright, L.: Serologic diagnois of epidemic typhus fever. Am. J. Epidemiol. 105: 261-271, 1977. Ormsbee, R.A. and Peacock, M.G.: Rickettsial plaques assay and cloning procedures. Tissue Culture Assoc. Manual 2: 475-478, 1976.